1. Field of the Invention
This invention relates to a method and apparatus for bonding lead wires or the like to pads and terminals of electronic elements and semiconductor devices, and to a method and apparatus for testing a bonded portion. More particularly, the invention relates to the bonding of a magnetic head, an LED, an EL, a liquid crystal, a thermosensitive head, etc.
2. Description of the Related Art:
According to the conventional technology, lead wires are connected to pads and terminals of electronic elements and semiconductor devices by soldering (including the reflow method), ultrasonic joining, hot pressing or resistance coupling. As one of the ultrasonic joining methods, ultrasonic bonding (wedge or ball) was particularly popular. In the joints of lead wires with pads and terminals of electronic elements and semiconductor devices, it is important to secure good quality and reliability; consequently, attempts have been made to develop a high-quality and high-reliability bonding technology.
To this end, there have been proposed various kinds of means for discriminating whether or not the individual bonded portion is good. This prior art is exemplified by: the concept of detecting a high-frequency current waveform from an ultrasonic generator and discriminating, by the current intensity and waveform, whether or not the bonded portion is good, as disclosed in Japanese Patent Laid-Open Publications Nos. SHO 61-237438, SHO 61-237440 and SHO 62-76731; the concept of detecting and discriminating an abnormality when the output and the vibrating time of an ultrasonic generator are outside the respective predetermined ranges, as disclosed in Japanese Patent Laid-Open Publication No. SHO 61-294830; and the concept of measuring the vibration of a bonding tool, by monitoring the ultrasonic wave during bonding, to detect a bonding status, as disclosed in Japanese Patent Laid-Open Publication No. SHO 62-293731.
Further, various high-reliability bonding methods and apparatuses have been proposed. This prior art is exemplified by: a bonding method in which the temperature of a lead wire heated by heat or light rays is measured by a non-contact thermometer, as disclosed in Japanese Patent Laid-Open Publication No. SHO 63-232438; a bonding method in which the position of a bonding tool is detected and then the movement of the bonding tool is controlled, as disclosed in Japanese Patent Laid-Open Publication No. SHO 63-257238; a bonding method in which the load during bonding is varied and controlled, as disclosed in Japanese Patent Laid-Open Publication No. HEI 1-129430; a bonding method in which the ultrasonic frequency and output are varied and controlled, depending on the bonding manner and position, as disclosed in Japanese Patent Laid-Open Publication No. HEI 1-184841; and a bonding method in which attenuation of ultrasonic vibration of a bonding tool is measured and the ultrasonic vibration is stopped when it becomes normal, as disclosed in Japanese Patent Laid-Open Publication No. HEI 2-156548.
Meanwhile, in testing and evaluating a bonding portion after it has been bonded, it is a common practice to observe the bonding portion with visual inspection by an operator. This prior art is exemplified by: the concept of detecting the width of bonding of a bonding portion and discriminating, by the detected width, whether or not the bonded portion is good as disclosed in Japanese Patent Laid-Open Publication No. SHO 55-59731; the concept of converting pictures, which are photographed by a low-magnification camera and a high-magnification camera, into binary images and detecting deviation of bonding, the diameter of a ball, the shape of a ball and peeling, as disclosed also in Japanese Patent Laid-Open Publication No. SHO 55-59731; and a semiconductor device which discriminate the quality of a bonding portion according to heights printed by bonding tool on which ridges in different width are formed as disclosed in Japanese Patent Laid-Open Publication No. HEI 1-273328.
However, the bonding apparatus of the prior art would occasionally be encountered with connection defects, such as lowered connection strength of the bonding portion and a peeled surface, so that the functions of semiconductor devices and electronic elements can be impaired or the defective products can be caused. Because of this, the apparatus is not entirely reliable.
On the other hand, with the prior means for discriminating whether or not the bonded portion is good, it is easy to inspect the bonded portion but is difficult to discriminate whether or not the bonded portion is very reliable. Consequently, it was impossible to secure the reliability and quality in connecting the bonding portions of lead wires with pads and terminals of semiconductor devices and electronic elements, so the defective products increased with the peeled surface, the lead wires at the bonded portion breaking off while in use, the functions of the semiconductor devices, electronic elements, etc. were deteriorated with increased connection resistance.
Further, in the prior testing method and apparatus, after bonding, the bonded portion is visually inspected by an operator, because this test depend on the operator's skill, it is difficult to grasp the connection quality of the bonded portion, causing a poor operativity and hence taking a long time to conduct a test.